Process for the beneficiation of taconite fines



Ofc. 9, i956 G KOMAREK ETAL 2,766,109

PROCESS FOR THE BENEFICIATION OF TACONITE FINES Filed Sept. 5, 1952 INVENTORS.'

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Kad R Jmezk 13/M440! ATTORNEYS PROCESS FOR THE BENEFICIATION OF TACONITE FINES Gustav Komarek and Karl R. Komarek, Chicago, lll., as-

signors to Komarek-Greaves and Company, Chicago, Ill., a corporation of Illinois Application September f, 1952, Serial No. 308,038

7 Claims. (Cl. 753) This invention relates to a process for the beneficiation of taconite fines whereby briquettes of exceptionally high density and great strength are produced, and which are thereby exceptionally Well suited for blast furnace operation.

It is an object of our invention to produce briquettes of taconite fines which are of high density and possess great strength by an ecient process of briquette manufacture which will possess great heat economy.

It is a further object of our invention to produce briquettes of taconite nes which, owing to their great density and their increased ability to absorb heat, will melt in the blast furnace more advantageously and, at the same time, have less tendency to disintegrate and yield small particles which would be blown out of the furnace.

It is an additional object of this invention to provide briquettes which, when heated in a blast furnace, Will produce a higher quality of iron.

It is another object of our invention to produce briquettes of taconite lines which, when piled in a heat treating furnace, will not squash in the same to cause interference of heat passage through the briquettes which is necessary for uniform heating.

It is still another object of our invention to produce briquettes of taconite nes possessing higher density and greater strength without resort to the use of higher than customary pressures in the briquetting machine.

The accompanying drawing is a schematic representation of the briquetting procedure employed in the subject invention.

With reference to the drawing, the raw and wet taconite lines contained in a bin 1 are fed to a conduit C by means of screw conveyor S into a turbulent stream of heated air or other gas, such as products of combustion or a mixture of air and products of combustion, supplied to conduit C by blower 2 and furnace 3. This gas stream conveys the fines to a cyclone separator 4 as shown. Contact between the turbulent stream of heated gas and the fine particles of taconite in the conduit C will almost instantly dry the taconite fines and heat them to the desired temperature. The turbulent stream of heated gas, resultant water vapor and dried and heated taconite fines is delivered tangentially into the cyclone separator 4, Where the taconite fines are separated from the gaseous mixture which accompanies them. The discharge end 5 of the cyclone separator 4 is positioned directly above and in direct communication with the nip 6 of two briquetting rolls 7 and S of a conventional briquetting machine 9 in which the rolls rotate in the direction indicated by the arrows.

The total elapsed time between the time the cold and wet taconite fines are fed to the stream of heated gas in the conduit C and the time the briquettes are discharged from the briquetting machine 9 is very short. Ten seconds is a very suitable time, although this figure is only an approximation, since less time may be employed with a faster briquetting machine, or more time if the fines are conveyed a considerable distance. The important cri- .Patented Oct. 9,- 1956 terion is that the fines be permitted to remain in contact with the turbulent heated gas for the few seconds necessary to effect drying and heating. A longer period of time may be employed, but since heat loss is a function of time and wall area of the transporting conduit C, it is not economically desirable to do this.

It was discovered that, while it was not possible to produce satisfactory briquettes from raw taconite fines, the same fines, after the treatment above recited, produced briquettes of high density and satisfactory mechanical strength.

The heating of the taconite fines, e. g., in the conduit C, should be preferably within the range of from about 200 F. tol 600 F. It was discovered that at approximately 200 F. the agglomerating tendency of the taconite nes became noticeably favorable while atlower temperatures the agglomerating tendency was highly unfavorable. This favorable tendency to produce stronger agglomerates of greater density continued to improve as the temperature increased. It was noted that although temperatures above 600 F. may be employed in the process, this is not economical because of the practical difficulties involved in heating air or other gas of the conveying gas stream to a temperature suiciently high kto yield taconite temperatures above 600 F. when the gas or the air and taconite are mixed in the conduit C.

The briquettes discharged from the briquetting machine 9 are fed immediately to a furnace such as a shaft type or a rotary kiln (not shown) for final heat treatment. The final heat treatment of the briquettes is conducted immediately after the briquettes are discharged so that the heat contained in the briquettes may contribute to heat economy for this final treatment.

In this final heat treatment, either a shaft-type furnace or a rotary kiln performs efficiently. A rotary kiln would serve to heat the briquettes more uniformly, but the particular heating equipment employed for the final heat treatment may vary considerably. The important feature is the fact that the briquettes discharged from the briquetting machine 9, after having been produced in accordance with the instant disclosure, have acquired such a preliminary strength and density that they will not squash or disintegrate to any appreciable extent from the pressure, jarring, tumbling, and heat to which they are subjected while piled in the heat treating furnace. This treatment hardens the briquette so that it will resist abrasion and withstand rough treatment.

The temperature for this final heat treatment may vary from about l000 F. to the fusion point, which may be as high as about 2400 F. It is preferable, however, to resort to temperatures which convert the magnetite in the taconite to hematite. The conversion of the magnetite in the taconite to hematite ordinarily takes place when temperatures in the range of 1400 to 1700 F. are reached. This conversion releases large quantities of heat, and this, together with the fact that the briquettes contain nearly all the heat from the primary heating of the taconite in the conduit C, makes the final furnace treatment economical. A preferable temperature is 19007 F., and the temperature range preferably may vary from about 1600 F. to 2400 F. The time period of the heat treating will, of course, vary with the temperature, a preferred time period being l5 minutes at l900 F.

It is observed that raising the raw taconite fines directly to a high enough temperature before briquetting to make the nal furnace heat treatment unnecessary, is an expensive operation. On the other hand, the primary heat treatment of the taconite fines in the conduit C is substantially instantaneous, e. g., less than about 10 seconds, and is a very low cost operation. Additionally, this primary heat treatment produces a highly beneficial improvement in the mechanical strength and density of the resulting briquettes.

The outstanding features of the product which results when the instant procedure is followed are its high density and great mechanical strength. The exact reasons for these improved results is not fully understood at present. The fact that the temperatures employed may be as low as approximately 200cl F. in the conduit C makes it highly unlikely that the improved properties achieved may be due to the occurrence of nascent plasticity although such occurrence may be the cause of the progressive improvement which occurs as higher temperatures are employed. Apparently, the almost perfect particle Contact which is achieved and which results in an exceptionally dense and strong product is in some way related to the speed at which the moisture is completely eliminated and the tem perature of the individual taconite particles is raised when suspended in a turbulent stream of heated gas or air. lt is feasible that this primary treatment causes increased molecular activity of the taconite which yields increased cohesion when the treated particles are subjected to pressure in the briquetting machine. That is, it is believed that the new and unexpected improved results are obtained by subjecting the taconite iines to a brief contact with a heated stream of gas or air in a manner which will dry and heat the nes in an extremely short time interval.

Other sources of heat economy can be realized by suitable insulation of the conduit leading to the cyclone separator, as well as insulation of the cyclone separator itself. The residual heat remaining in the gas which is discharged from the top of the separator may be employed to pre-heat the air used in the process, or this gas may itself be recycled to the blower. A final source of heat economy can be realized by utilizing the residual heat in the resulting briquettes to heat the air or gas employed in the process.

Having thus described our invention, what we claim is:

1. A process for the beneiciation` of taconite fines which comprises subjecting raw and wet taconite iines to simultaneous heating and drying in contact with a stream of heated gas, non-reactive with taconite at the heating temperature, the gas beingrheated to a temperature sufciently high to heat the fines to a temperature of between 200 F. and 600 F. within a few seconds, separating the gas from the dried and heated taconite fines, and immediately pressing the separated fines into briquettes.

2. A process as recited in claim 1 in which the briquettes so produced are immediately heated to at least 1000 F.

3. A process as recited in claim 1 in which the briquettes so produced are immediately heated to a temperature suiciently high to convert the magnetite present in the taconite to hematite.

4. A process according to claim 1, in which the gas 1s air.

5. A process according to claim l, wherein the time of Contact of the taconite fines and the heated gas is not over about 10 seconds.

6. A process according to claim l, in which the briquettes so produced are immediately heated to a temperature between about 1400 to 1900 F.

7. The process of claim 6, in which the briquettes are heated without added material.

References Cited in the le of this patent UNITED STATES PATENTS 

1. A PROCESS FOR THE BENEFICIATION OF TACONITE FINES WHICH COMPRISES SUBJECTING RAW AND WET TACONITE FINES TO SIMULTANEOUS HEATING AND DRYING IN CONTACT WITH A STREAM OF HEATED GAS, NON-REACTIVE WITH TACONITE AT THE HEATING TEMPERATURE, THE GAS BEING HEATED TO A TEMPERATURE SUFFICIENTLY HIGH TO HEAT THE FINES TO A TEMPERATURE OF BETWEEN 200* F. AND 600* F. WITHIN A FEW SECNDS, SEPARATING THE GAS FROM THE DRIED AND HEATED TACONITE FINES, AND IMMEDIATELY PRESSING THE SEPARATED FINES INTO BRIQUETTES. 